Bone metastases are a common cause of morbidity in cancer patients. The debilitating pain that occurs in many patients with advanced malignancies is primarily produced by bone metastases. Spinal metastases can produce cord compression and severe neurologic impairment. Many malignancies can result in bone metastases including breast cancer (median survival time is 20 to 30 months), lung cancer (median survival of less than 6 months), and prostate cancer (the second leading cause of cancer deaths in men in the United States) account for more than 80% of bone metastases. Conversely, more than 50% of patients with these primary cancers will eventually develop bone metastases (Malawer and Delaney In: DeVita, et al., eds. Cancer: Principles and Practice of Oncology. Philadelphia: JB Lippincott Company, 4th Edition, 1993, pp 2225–2245).
The management of bone metastases depends on a number of factors: the location and extent of bony destruction, the severity of morbidity, the availability of effective systemic therapies (hormonal or chemotherapy), and the overall status of the patient. Bisphosphonates have been shown to promote healing and lessen pain in patients with osteolytic metastases (van Holten-Verzantvoort, et al. (1987) Lancet 2(8566):983–985; Elomaa, et al. (1985) Lancet 1(8438): 1155–1156). Some hematologic malignancies that involve bone, particularly the lymphomas, may be cured with systemic hormonal therapy or radiotherapy, but for most patients with bone metastases, palliation is the goal of therapy. Radioisotopes such as strontium-89 and samarium-153 have been shown to decrease pain in patients with osteoblastic metastases resulting from prostate cancer (Robinson (1993) Cancer 72(Suppl.):3433–3435; Bolger, et al. (1993) Seminars in Oncology 20(Suppl. 2):32–33).
There is a need in the art for effective combined therapies capable of placing advanced stage widespread metastases into remission.
ATP has as physiological role in aging and tumor development. Lowered contents of adenine compounds in the erythrocytes and thrombocytes obtained from patients with various neoplastic malignancies has been observed (Laciak and Witkowski (1966) Otolaryngol Pol. 20(2):269–75; Wand and Rieche (1972) Dtsch Gesundheitsw. 27(23):1072–6; De la Morena Garcia, et al. (1977) Rev. Clin. Esp. 146(5):221–3; Stocchi, et al. (1987) Tumori 73(1):25–8). Likewise, human blood ATP levels decline as individuals age (Rabini, et al. (1997) Eur. J. Clin. Invest. 27(4):327–32). Furthermore, there exists a relationship between aging and the development of cancer (Henson and Tarone (1994) Cancer 74(1 Suppl):424–9; Braendle (2000) Ther. Umsch. 57(10):646–50; Kikuchi, et al. (2000) Jpn. J. Cancer Res. 91(8):774–9; Cortopassi and Wang (1996) Mech. Ageing Dev. 91(3):211–8; Liu, et al. (1994) Proc. Natl. Acad. Sci. USA 91(19):8910–4).
The genetic disease Cystic Fibrosis (CF) is associated with elevated levels of blood ATP. Age-adjusted rates of prostate, breast and other tumors were shown to decrease in individuals homozygous for the CF defect and who had elevated blood ATP levels (Warren, et al. (1991) BMJ 302(6779):760–1; Padua, et al. (1997) Hum. Mutat. 10(1):45–8; Neglia, et al. (1995) N. Engl. J. Med. 332(8):494–9; Abraham, et al. (1996) Nat. Med. 2(5):593–6; Miro and Orecchia (2002) Lancet Oncol. 3(7):395).
An inverse relationship exists between exercise and tumor development in experimental animals (Daneryd, et al. (1998) Cancer Res. 58(23):5374–9; Daneryd, et al. (1990) Eur. J. Cancer 26(10):1083–8; Daneryd, et al. (1995) Eur. J. Cancer 31A(13–14):2309–12; Fishman, et al. (1998) Cancer Res. 58(14):3181–7). In exercising rats, tumor volumes are significantly reduced in a manner inversely related to tumor ATP pools. Exercising human muscles release significant amounts of adenosine and ATP (Hellsten, et al. (1998) Circulation 98(1):6–8; Hellsten, et al. (1998) Am. J. Physiol. 274(4 Pt 1):E600–6). It was found that tumor metastases to striated muscle are clinically rare. The elevations in ATP and its catabolic products, ADP, AMP and adenosine were directly analyzed in the interstitium of exercising skeletal muscle and these elevations were directly related to the level of work performed by the muscle. A recent study concluded that low molecular weight factors, which are released by muscle cells and are inhibitory to tumor development and growth, were adenosine and its related compounds (Fishman, et al. (1998) Cancer Res. 58(14):3181–7). Therefore, extracellular purine levels are important in modulating tumor growth.
The significant depletion of host visceral energy stores by a growing tumor has been demonstrated in experimental animals (Inculet, et al. (1987) J. Natl. Cancer Inst. 79(5):1039–46; Peacock, et al. (1987) Surgery 102(3):465–72; Schneeberger, et al. (1989) Cancer Res. 49(5):1160–4). Along with the decline in hepatic ATP pools in cachexia tumor animal models, severe declines in skeletal muscle ATP pools were demonstrated (Inculet, et al. (1987) J. Natl. Cancer Inst. 79(5):1039–46; Peacock, et al. (1987) Surgery 102(3):465–72; Schneeberger, et al. (1989) Cancer Res. 49(5):1160–4; Daneryd, et al. (1998) Cancer Res. 58(23):5374–9; Daneryd, et al. (1995) Eur. J. Cancer 31A(13–14):2309–12).
Relatively low levels of extracellular ATP inhibit the growth of a variety of human tumor cells and subsequently yield substantial cell killing in in vitro systems (Rapaport, et al. (1983) Cancer Res. 43(9):4402–6). The mechanism of tumor cell killing is attributed to the permeation of tumor cell membranes by extracellular ATP and the arrest the tumor cells in S-phase followed by cell death (Schroder and Rapaport (1984) J. Cell Physiol. 120(2):204–10; Rapaport, et al. (1983) J. Cell Physiol. 114(3):279–83). Nucleoside analogues and derivatives thereof are anti-tumor agents (U.S. Pat. Nos. 4,291,024; 4,880,918; and 5,641,500; Galmarini, et al. (2002) Lancet Oncol. 3:415–424; Janssens and Boeynaems (2001) Br. J. Pharmacol. 132:536; Fang, et al. (1992) J. Clin. Invest. 89:191). Radiolabeled adenine nucleotides also arrest the growth of tumor cells (U.S. Pat. Nos. 5,049,372). ATP- and diethylmaleate (DEM)-treated mice receiving a single dose of irradiation exhibit a reduction in viable cancer cells (Estrela, et al. (1995) Nature Medicine 1:84–88). However, without the thiol-depleting agent (DEM) radiation alone is not enough to eliminate cancer cells in tumor-bearing mice treated with ATP. Furthermore, ATP-induced glutathione depletion in combination with recombinant human tumor necrosis factor (rhTNF-α) results in a 61% inhibition of tumor growth (Obrador, et al. (1997) Biochem. J. 325:183–189).
In addition to its inherent cytolytic activities, extracellular ATP enhances the penetration of chemotherapeutic agents such as doxorubicin (Maymon, et al. (1994) Biochim. Biophys. Acta 1201(2):173–8) or vincristine (Mure, et al. (1992) Jpn. J. Cancer Res. 83(1):121–6) into tumor cells, significantly enhancing cell killing.
Extracellular ATP is a potent trigger of cell killing not only for tumor cells but also of associated endothelial cells that comprise the tumor vasculature. Extracellular ATP activates the transcription factor NF-kappa B through activation of the P2Z receptors. The ATP-induced generation of NF-kappa B leads to endothelial cell apoptotic death (von Albertini, et al. (1998) Biochem. Biophys. Res. Commun. 248(3):822–9; von Albertini, et al. (1997 Transplant Proc. 29(1–2):1062). Furthermore, U.S. Pat. No. 6,436,411 discloses the use of ATP to activate monocytes or macrophages to induce those cells to produce a number of immune stimulatory molecules including cytokines which may be used to treat cancer.